A typical operating system includes a file system. The file system provides a mechanism for the storage and retrieval of files and a hierarchical directory structure for the naming of multiple files. More specifically, the file system stores information provided by the user (i.e., data) and information describing the characteristics of the data (i.e., metadata). The file system also provides extensive programming interfaces to enable the creation and deletion of files, reading and writing of files, performing seeks within a file, creating and deleting directories, managing directory contents, etc. In addition, the file system also provides management interfaces to create and delete file systems. File systems are typically controlled and restricted by operating system parameters. For example, most operating systems limit the maximum number of file names that can be handled within their file system. Some operating systems also limit the size of files that can be managed under a file system.
An application, which may reside on the local system (i.e., computer) or may be located on a remote system, uses files as an abstraction to address data. Conventionally, this data is stored on a storage device, such as a disk.
Data stored as files in a file system may be replicated using one or more replication schemes. Replication schemes are typically used to enable recover data in the event of file system failures, data corruption, etc. Data replication ensures continuous availability and protection of data stored on disk. The follow is a non-exclusive list of common replication schemes: redundant arrays of independent disks (RAID) schemes, 2-way mirroring, 3-way mirroring, etc. Typically, the level of granularity available for replication of data is a file.
There are many RAID schemes currently available. One common RAID scheme is RAID-5. In general, RAID-5 is used to replicate data across multiple physical disks organized in an array. More specifically, the physical disks in the data storage system are typically segmented into blocks of data space. A block may comprise any appropriate number of bytes of data (e.g., 512 bytes, 1024 bytes, etc.). In RAID-5, data to be stored is divided into data blocks and the resulting data blocks are XORed to obtain a parity block. The parity block corresponds to a block that is used to recover part of the data in the event that one of the aforementioned data blocks is corrupted or the disk, upon which the data block is stored, fails. The data blocks and the parity block are then written to the multiple disks by striping the data blocks across the multiple disks.
As discussed above, the parity block is used to reconstruct a block of data, if the block of data becomes corrupted or is not accessible (e.g., the disk upon which it is stored is offline). In such cases, the volume manager is notified that the disk has failed. Once the volume manager knows the disk has failed, it may then proceed to use the parity bit along with the other data blocks to reconstruct the corrupted data block.